This report published by the Rand Policy Research Center examines the effects of the Affordable Care Act on the provision of health care at small businesses.  

From the report:

The recently enacted federal health care reform law (the Affordable Care Act, or ACA) is designed to increase the number of Americans covered by health insurance. One way it does this is by creating health insurance exchanges, which are new markets for purchasing insurance. It also imposes fines on certain employers that do not offer coverage and on individuals who do not have public or private insurance (known as the individual mandate). Employers with 50 or fewer workers are exempt from fines. By 2016, firms with 100 or fewer employees will be allowed to purchase coverage for employees through the insurance exchanges. However, there is considerable debate about the likely effect of these provisions in the law.

Full Report: How will the Affordable Care Act Affect Employee Health Coverage at Small Businesses? (PDF | 86 KB)   

Rand Policy Research Center. (2010). How will the Affordable Care Act affect employee health coverage at small businesses?. Eibner, C., McGlynn, E., Girosi, F., Price, C., Cordova, A., Hussey, P., and Beckman, A.